Although cataracts originate from several different pathologies, their common manifestation is an opacity of the crystalline lens of the eye which either impairs or obstructs the vision of an afflicted individual. In any event, there are several well known cataract surgical procedures which can be performed to alleviate or eliminate the problem. The most radical of these procedures is a lentectomy. In a lentectomy, the opaque crystalline lens is effectively removed from the lens capsule. It is then replaced with an acrylic or plastic lens. Most commonly, the lentectomy is performed by using a knife to cut the lens out of the lens capsule. Recently, however, procedures have been suggested wherein laser energy is used to remove the cataractous tissue from the lens capsule.
U.S. Pat. No. 4,538,608 which issued to L'Esperance, Jr. for an invention entitled "Method and Apparatus for Removing Cataractous Lens Tissue by Laser Radiation" is an example of a device which employs laser energy to perform a lentectomy. According to the teachings of L'Esperance, laser energy is directed onto the anterior aspect of the cataractous lens tissue and the laser beam is then scanned within a limiting perimeter until the cataractous tissue has been photoablated. In accordance with this procedure, the cataractous tissue in the lens is removed in sheets from the anterior aspect of the lens toward the posterior capsule. An adverse consequence of this approach is that it is necessary to continually be working through a fragmented layer of lens tissue which scatters light and thereby causes unwanted inefficiencies.
The present invention, however, recognizes that the anatomy of the lens tissue in the eye, and the reaction of this tissue to photoablation, permits a procedure for removing cataractous tissue from the lens capsule which is quite different from the procedures suggested by L'Esperance. To appreciate this, it is first necessary to understand the anatomy which is being treated.
The lens of an eye is a transparent biconvex body of crystalline tissue which is situated between the posterior chamber and the vitreous body. It is enclosed within a lens capsule and it constitutes part of the refracting mechanism of the eye. The structure of the tissue in the lens includes a lens nucleus which is surrounded by the lens cortex. More specifically, the lens cortex includes separate envelope-like layers of tissue which completely surround the nucleus and all other layers which are located closer to the nucleus. The result is that the lens, in cross section, exhibits an anatomy that structurally appears somewhat like an onion.
As recognized by the present invention, the use of a laser beam to make a plurality of minute incisions throughout the cataractous lens tissue will accomplish at least two results that facilitate the removal of the tissue from the lens capsule. Firstly, such incisions assist in mechanically separating the cataractous lens tissue into small particles. Secondly, the vapors which are released during the photoablation of the incisions will infiltrate between the layers of the lens and will act to liquify the lens tissue. Together, the mechanical separation of the tissue and the tissue liquification process which results from photoablation, appropriately alter the cataractous tissue so that it can be aspirated from the lens capsule.
In light of the above it is an object of the present invention to provide a method for using a laser beam to remove cataractous tissue from the lens capsule of an eye which is accomplished by creating a plurality of minute incisions throughout the cataractous tissue that will separate and liquify the lens tissue to facilitate its removal from the lens capsule. Another object of the present invention is to provide a method for using a laser beam to remove cataractous tissue from the lens capsule of an eye which is accomplished by appropriately confining photoablation within the confines of the lens capsule. Still another object of the present invention is to provide a method for using a laser beam to remove cataractous tissue from the lens capsule of an eye which is accomplished by efficiently using laser energy to photoablate cataractous tissue. Another object of the present invention is to provide a method for using a laser beam to remove cataractous tissue from the lens capsule of an eye which is accomplished by focusing the cutting laser beam through unfragmented tissue to reduce light scattering and improve laser efficiencies. Yet another object of the present invention is to provide a method for using a laser beam to remove cataractous tissue from the lens capsule of an eye which is safely accomplished by continuously referencing the position of each incision into the cataractous lens tissue. Another object of the present invention is to provide a method for using a laser beam to remove cataractous tissue from the lens capsule of an eye which is relatively simple to accomplish and which is comparatively cost effective.